Sound masking systems basically include a masking sound generator, an equalizer, a power amplifier and one or more loudspeakers.
As sound masking systems are being developed, it is now known that efficiency thereof is linked to their ability to emit an ideal masking noise spectrum with an adequate precision. The ideal masking noise is defined as achieving optimized speech privacy at a listener's position for example (Acoustical Design of Conventional Open Plan Offices, 2003).
A main challenge remains in adjusting this ideal spectrum to any target environment, taking into account a number of parameters including a size of the room, a coating of the walls of the room, the furniture of the room and the ambient noise for example. The masking noise is usually adjusted manually by 1 octave equalization or ⅓ octave equalization, which proves to be sufficient in cases of simple environments, for example in the case of a building with a very uniform construction with a limited number of masking loudspeakers. However, such a trial and error method is laborious and often yields poor results in the cases of larger environments. Indeed, larger masking systems may cover more than one room or workplace in a building for example, and each may need a specific masking sound level control.
U.S. Patent No. 4,438,526 to Thomalla, issued in 1984, discloses an automatic volume and frequency controlled sound masking system, wherein a masking noise is generated by a set of analog filters, and is adjusted during emission thereof, according to a noise measured by microphones. This system modifies the level and spectra of the sound masking noise generated in a room according to a background noise level in the room, by increasing the masking noise when the back ground noise increases. When there is no other noise, such as noise due to the activity of workers for example, in the room other than the background noise, the masking noise level and spectra generated by the system done according to a preset voltage. The preset voltage is adjusted manually to provide a predetermined DC output and thus a predetermined background noise level (the resulting masking noise) when the room is otherwise quiet.
In spite of these efforts, there is room in the art for an auto-adjusting sound masking system and a method allowing emitting a target masking noise.